1. Field of the Invention
The present invention relates to a high speed, objective optical system of an economical construction and more particularly a multi-element thin objective system capable of providing video projection.
2. Description of the Prior Art
Since approximately the invention of television, attempts have been made to increase the size of the viewing picture. Simple glass magnification lenses were initially introduced to directly enlarge the size of the images on the cathode tube with the viewer observing the object side of the lens. Improvements in the resolution and size of cathode tubes made these early efforts obsolete.
Recently, various forms of television projection lens systems have been suggested. These T.V. projection systems have become popular particularly in commercial environments and to a lesser degree in individual residences. A prime problem for universal acceptance revolves about the factors of cost and image quality. The aberrations created in the magnification of the image during projection have required relatively expensive solutions.
A popular, but expensive, approach has been called a Schmidt system since it utilizes a Schmidt catadioptric objective system. The complimentary video system for the Schmidt system is specifically designed as an integral component and it is possible to drive its cathode tube to temperatures beyond those permitted on a normal television set to increase the illumination.
Recently, a triplet objective system with aspheric surfaces has been suggested. The lens elements of this system are formed from plastic and are relatively thick requiring special efforts during production with resulting costs.
Various types of curved Fresnel lenses for special optical applications have been suggested in the optical field and are cited of general interest such as U.S. Pat. Nos. 3,653,751; 3,572,903 and 3,523,721.
The prior art is still striving to provide a relatively inexpensive objective lens system that can be mounted on the average television set to provide a magnified projection of the video images onto a viewing screen with acceptable image resolution.